As one of technologies to increase the communication speed of mobile stations located at cell edges, DC-HSDPA (Dual Cell-HSDPA operation) using existing HSDPA (High Speed Downlink Packet Access) has been examined in 3GPP (3rd Generation Partnership Project). DC-HSDPA uses two frequency channels (each of which is 5 MHz) contained in the same frequency band in order to increase the downlink speed. The general idea of DC-HSDPA, which has been currently examined in 3GPP, is explained hereinafter. Note that the details of DC-HSDPA technique, which has been currently proposed, are explained in Non-patent literatures 1 to 3 cited below.
In DC-HSDPA, a second serving HS-DSCH cell is referred to as “secondary-serving HS-DSCH cell”. Meanwhile, a first serving HS-DSCH cell is simply referred to as “serving HS-DSCH cell”. A secondary-serving HS-DSCH cell is dependently formed on condition that a serving HS-DSCH cell is already generated. Note that the serving HS-DSCH cell may be also referred to as “primary carrier” or “base carrier”. Meanwhile, the secondary-serving HS-DSCH cell may be also referred to as “secondary carrier” or “extended carrier”.
In this specification, in order to clearly distinguish between these two serving HS-DSCH cells, the first serving HS-DSCH cell is referred to as “primary-serving HS-DSCH cell”. Further, in the following explanation, the primary-serving HS-DSCH cell and the secondary-serving HS-DSCH cell may be also referred to as simply “primary cell” and “secondary cell” respectively. Further, to distinguish the secondary cell from other cells, the primary cell and a non-HSDPA cell are collectively referred to as “non-secondary cell”. The non-HSDPA cell is an ordinary cell generated by a base station that supports neither HSDPA nor DC-HSDPA.
FIG. 13 shows physical channels used to perform packet communication with DC-HSDPA between a base station (Node B) 91 supporting DC-HSDPA and a mobile station 92. HS-PDSCH is a downlink physical channel for data transmission, and transfers a transport channel HS-DSCH. HS-SCCH is used for transmission of downlink signaling information about HS-DSCH transfer. HS-DPCCH is an uplink physical channel used to transmit, from the mobile station 92 to the base station 91, feedback information about HS-DSCH transfer. This feedback information includes an ACK response regarding a hybrid ARQ (Automatic repeat-request), and a CQI (channel Quality Indication). The uplink DPCH and downlink DPCH are used to transmit/receive control information about DC-HSDPA. Needless to say, other common physical channels indispensable to the generation of the primary cell (such as P-CPICH, SCH, P-CCPCH and S-CCPCH) and common physical channels indispensable to the generation of the secondary cell (such as P-CPICH and SCH) are also used. The formal names of these physical channels and transport channels, which are shown above in abbreviated names, are shown below
P-CPICH: Primary Common Pilot Channel
DPCH: Dedicated Physical Channel
HS-DPCCH: Dedicated Physical Control Channel (uplink) for HS-DSCH
HS-DSCH: High Speed Downlink Shared Channel
HS-PDSCH: High Speed Physical Downlink Shared Channel
HS-SCCH: Shared Control Channel for HS-DSCH
P-CCPCH: Primary Common Control Physical Channel
S-CCPCH: Secondary Common Control Physical Channel
SCH: Synchronisation Channel
When two serving HS-DSCH cells are established in a base station supporting DC-HSDPA, the activation and deactivation of the secondary cell are controlled by the base station. A command (HS-SCCH Order) that is used by the base station to instruct a mobile station (UE) on the activation and deactivation of the secondary cell is transmitted to the mobile station by using HS-SCCH, which is a downlink control channel. Further, the activation and deactivation of the secondary cell may be also changed by transmitting an RRC message from the base station or a radio network controller (RNC) to the mobile station. The details of the message structure and the like of the RRC MESSAGE are explained in 3 GPP TS 25.331 V8.4.0 (2008-09) “Radio Resource Control (RRC)”.
Meanwhile, as the indoor voice communication and data transmission have grown in demand owing to the widespread use of mobile phones, the development of compact base stations that can be installed in user's houses, offices, and the likes has been under way. These compact base stations are installed in houses, small-scale offices, and the likes by the owners of the compact base stations, for example, and are connected to an upper layer apparatus on core-network sides by using ADSLs (Asymmetric Digital Subscriber Lines) and fiber-optic lines. In 3GPP, the standardization task has been under way while defining these compact base stations as “Home NodeB” and “Home eNodeB” (for example, see Non-patent literature 4). Note that “Home NodeB” is a compact base station for use in UMTS (Universal Mobile Telecommunications System), while the “Home eNodeB” is a compact base station for use in LTE (Long Term Evolution). In this specification, these compact base stations are referred to as “home base stations”, and cells generated by these home base stations are referred to as “home cells”.
In base stations used in existing mobile communication networks (cellular communication networks), radio resources to be used in communications between the base stations and mobile stations are determined in advance. In contrast to this, as for the home base stations, a technique to make a home base station autonomously select a radio resource has been examined. Note that the radio resources mean frequency channels in FDMA (Frequency Division Multiple Access) systems, whereas they mean spreading codes in CDMA (Code Division Multiple Access) systems. In the case of 3GPP UMTS (W-CDMA: Wideband-CDMA), the radio resources mean frequency channels and scrambling codes. Further, in the case of 3GPP LTE in which SC-FDMA (Single Carrier FDMA) is used for the uplink and OFDMA (Orthogonal FDMA) is used for the downlink, the radio resources means physical resource blocks. The physical resource block is the unit of the radio resources used for downlink data transmission from a base station to a mobile station, and includes a plurality of OFDM subcarriers in the frequency domain and at least one symbol time in the time domain.
Patent literature 1 discloses a home base station that receives a permission list including a plurality of radio resource candidates (specifically, frequency channels and scrambling codes) from an administration system to which the home base station is connected through an xDSL line, a fiber-optic line, or the like, and measures a received signal strength and a CIR (Carrier to Interference Ratio) of a radio signal for each of the radio resource candidates included in the permission list. Further, the home base station disclosed in Patent literature 1 autonomously select a radio resource candidate having the lowest received signal strength and uses the selected radio resource for communication with a mobile station. The reason why the radio resource candidate having the lowest received signal strength is selected is that, by doing so, the interference with cells formed by nearby base stations is believed to be minimized. Further, the home base station disclosed in Patent literature 1 determines the initial transmission power of transmission using the selected radio resource by using the previously-measured received signal strength and CIR. Specifically, the initial transmission power is determined with consideration given to the interference level from the nearby base stations so that satisfactory communication service can be provided in a desired communication range (e.g., within 20 m).